Communication systems generally include a plurality of communication units, such as mobile or portable radio units, that are geographically distributed among various base sites. The communication units wirelessly communicate with the base sites and each other, and are often logically divided into various talkgroups. Communication systems may be organized as trunked systems, where a plurality of radio frequency (RF) communication resources are allocated amongst multiple users or groups by assigning the base sites and RF channels within a coverage area on a call-by-call basis, or as conventional (non-trunked) systems where RF communication resources are dedicated to one or more users or groups. In trunked systems, or in mixed trunked and conventional systems, there is usually provided a central controller/server (sometimes called a “zone controller”) for allocating RF communication resources among a group of sites. The zone controller may reside within a single device or multiple devices and may be located at a fixed equipment site or may be distributed among the base sites.
Typical communications systems, such as those in compliance with Association of Public-Safety Communications Officials-International (APCO) Project 25 standards, transmit data messages amongst the communication units and base sites using preset packet data channels (“also referred to herein as classic packet data channels”). These classic packet data channels are used to provide unscheduled delivery of data in both the inbound and outbound directions. More specifically, whenever a communication unit needs to transmit a data message, the communication unit checks whether the inbound packet data channel (i.e., the channel used for data communications from the communication units to a base site) is busy or idle. In APCO Project 25 systems, this is typically accomplished by reference to status symbols transmitted on the outbound packet data channel (i.e., the channel used for data communications from a base site to the communication units) that identify the status of the inbound packet channel. The specific protocols for such status symbols in an APCO Project 25 system are described in Telecommunications Industry Association (TIA) 102.BAAD.
Once the communication unit determines that the inbound packet data channel is idle, the communication unit attempts to transmit the data message. However, in communication systems that employ a large number of communications units occupying the same packet data channel, it is often the case that multiple communication units attempt to transmit a data message at the same time. This results in the deterioration or loss of the data messages transmitted from each of these multiple communication units.
Additionally, because data message transmissions are prone to such failures, communication systems also typically require a confirmation message be sent from the receiving device back to the originally transmitting communication unit on the outbound packet data channel to confirm receipt of the data message. This utilizes a significant amount of bandwidth on the outbound packet data channel.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of various embodiments of the present disclosure. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are not often depicted in order to facilitate a less obstructed view of these various embodiments of the present disclosure. It will be further appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein are to be defined with respect to their corresponding respective areas of inquiry and study except where specific meaning have otherwise been set forth herein.